Such semiconductor devices as ICs, transistors and light-emitting diodes are generally manufactured in the following process.
First, a semiconductor chip is bonded to a frame for manufacture (hereinafter referred to as frame), which is prepared by stamping a thin metal sheet to a predetermined shape. Then, wire bonding between leads formed to be integral with the frame at positions near the semiconductor chip and a bonding pad thereon is carried out by using a gold wire or the like. The eventual product thus obtained is then provided with a resin molding to enclose the semiconductor chip and the wire bonded region. Then, one removes the unnecessary portions of the frame and forms the leads. Then, after a mark formation step or an inspection step, each unit semiconductor device with leads projecting from a resin molding package portion is cut apart from the frame.
The frame is obtained from a thin sheet of iron plated with copper or a thin sheet of copper plated with nickel or silver. Further, since the wire bonding is made by using a gold wire, the lead portions for carrying out the wire bonding thereon are usually provided with gold plating in addition to the above plating. Such multiple layer plating on the base metal is done in order to prevent oxidization of the lead frame base layer. The silver plating as the outermost layer or further gold plating thereon is done to ensure the reliability of connection of the bonding wire to the leads.
As shown, in the prior art process of manufacture of semiconductor devices, it a prerequisite that the wire bonding to the leads is effected on gold plating (or sometimes on silver plating). Therefore, the entire frame has to be plated with nickel or silver and further with gold, if necessary. The process for such plating has been extremely complicated and increases the cost of the product.
In a further aspect, the wire bonding using a gold wire has to be done on a lead having a smooth surface. This means that the frame must be prepared with a minimum degree of smoothness. This has been a further cause of the increased cost of the product.
A primary object of the invention is to provide a semiconductor device, which has a novel wire bonding structure free from the conventional plating process that has been necessary for the gold wire bonding to leads on a frame.
Another object is to provide a method permitting efficient manufacture of such semiconductor device.